Barely a month into the new academic year, public school districts across the U.S. are already running short of a critical asset: teachers. In response, some states have lowered the standards for obtaining a teaching license — or eliminated the requirement altogether. There are better ways to help supply meet demand.

Turning over classrooms to noncredentialed, inexperienced teachers will do students more harm than good. The goal should be to raise standards, not abandon them. Policymakers should focus on subject areas where the need for qualified instructors is greatest, and on how to make it easier for teachers to take their credentials across state lines.

It is hardly unusual for districts to face teaching shortages; according to the U.S. Department of Education, all 50 states and the District of Columbia have at least some unfilled positions. Because of high attrition rates, U.S. schools must hire an additional 90,000 new teachers every year, but it’s not as if there’s a lack of college graduates with teaching degrees.

The problem is that there aren’t enough teachers in places and subjects where they’re most needed. Unsurprisingly, schools in low-income, rural and inner-city districts have the most trouble attracting certified teachers. Even in more affluent regions, there are too few candidates qualified to teach in the STEM subjects: 48 states say they’re unable to find enough teachers certified to teach math and 43 report shortages of science teachers.

There are market-based ways to address the problem — mainly, offering valuable teachers more money — but the districts most in need are usually the least able to afford them.

States also need to make it easier for teachers to relocate to where the jobs are. Only six states grant full teaching privileges to teachers with out-of-state licenses, without additional coursework or exams. That means teachers rarely cross state lines and are more likely to leave the profession altogether when they do.

The most sensible solution is to create a common teacher-licensing system, under which states would agree to shared standards and recognize credentials earned in other states. A bill in Congress, the Interstate Teaching Mobility Act, would require participating states to honor out-of-state licenses and create a single electronic application process for qualified teachers.

Giving teachers more freedom to move — and helping the market pay them what they’re worth — will help more students get the education they deserve.